A Study On Mosquito As A Primary Malaria Vector

Project and Seminar Material for Microbiology

Project and Seminar Material for Microbiology


Abstract


Malaria is a major problem in Nigeria with the highest prevalence of malaria in pregnancy of 64.5 percent. Little is known about the major malaria vector and its role in malaria transmission. This was a study on mosquito as a primary malaria vector. A total of 1030 female Anopheles mosquitoes were caught consisting of five species, namely, 1026 (99.6%) of Anopheles gambiae complex further identification using PCR showed the predominant sibling species were An. arabiensis Patton 95%(n=221) and An. gambiae s.s. 5%(n=12). Other Anopheles mosquitoes collected were morphologically identified as An. pharoensis, An. squamosus and An. rhodesiense.

Results showed that the population of Anopheles arabiensis was significantly higher than that of Anopheles gambiae s.s (P<0.05). In planning effective site specific malaria vector control programmes under the Integrated Vector Management (IVM) program of the Federal Government of Nigeria, results of this study has highlighted the need to give special consideration to the predominance of a single malaria vector An. arabiensis in the Sudanosahel and the strong seasonality of malaria in contrast to other regions of Nigeria. Findings also demonstrated the potentials of pyriproxyfen as an effective mosquito’s larvicide for consideration under the Integrated Vector Management (IVM) program for use in Nigeria.


Table Of Content


Preliminary Page(s)

  • Title page
  • Certification page
  • Dedication
  • Acknowledgement
  • Abstract
  • Table of content

Chapter One

1.0 Introduction

  • 1.1 Background Of The Study
  • 1.2 Mosquito Breeding Sites For Different Mosquito Types
  • 1.3 Aims And Objectives

Chapter Two

2.0 Literature Review

  • 2.1 Mosquito
  • 2.2 Concept Of Malaria
  • 2.3 The Malaria Parasite And Its Life Cycle
  • 2.4 Malaria Transmission

Chapter Three

3.0 Materials And Methods

  • 3.1 Entomological Investigation
  • 3.2 Human Parasitological Investigation
  • 3.3 Laboratory Evaluation Of Pyriproxyfen
  • 3.4 Data Analysis

Chapter Four

4.0 Results And Discussion

  • 4.1 Results
  • 4.2 Discussion

Chapter Five

5.0 Conclusion And Recommendation

  • 5.1 Conclusion
  • 5.2 Recommendations
  • References

Chapter One


1.0 Introduction

1.1 Background Of The Study

Mosquitoes are vectors of Plasmodium parasite that cause malaria, nematode worms that cause filariasis for example Wuchereria bancrofti, and a large number of arbo-viruses e.g yellow fever and dengue viruses including two of great impacts in the tropical ad sub-tropical regions (Ifeyinwa et al, 2012). They belong to the Order:Diptera and possess short elongated and slender body, long many-segmented antennae, long slender legs and an elongated proboscis with piercing and sucking mouth parts (Jordan et al, 2007).

Mosquitoes exploit almost all types of lentic aquatic habitats for breeding and some have been found to thrive in aquatic bodies such as fresh or salt water marshes, mangroves swamps, rice fields, grassy ditches, edge of streams and rivers and small temporary pools, (Oyewole et al, 2009). Many species prefer habitats with vegetations while some breed in open, sunlit pools. A few species breed in tree holes or the leaf axils of some plants (CDC, 2004).

Vector-borne diseases particularly mosquito-borne diseases have been the most important worldwide health problems for many years still represents a constant and serious risk to a large part of the world’s population. Mosquitoes rank as man’s important pest and most of the challenges posed by mosquito-borne diseases consist not only in their cosmopolitan nature and ability to survive in air, aquatic and terrestrial habitats, but their ability to breed in any collection of standing water such as wheel barrow, cesspits, flower vest and drainage systems make such a prolific source of mosquito production (Ifeyinwa et al, 2012).

Mosquito – transmitted diseases are the major cause of morbidity and mortality in sub Saharan Africa for example, there are up to 500 million clinical cases about deaths due to malaria globally (Olaleye et al, 2001).


1.2 Mosquito Breeding Sites For Different Mosquito Types

Breeding site is a place where mosquito can find all the physical and chemical requirements necessary for their growth, development and survival. Breeding sites vary according to types of mosquito. For example many species of Anopheles prefer habitats with vegetation while some breed in open, sunlit pools. A few species breed in tree holes or the leaf axils of some plants (CDC, 2004).

Anopheline species are known to be ground pool breeders, although large numbers have been observed in gutters, periodomestic run off and domestic containers (Mafiana et al, 1998; Aigbodion et al, 2003). Anopheles mosquito has been found to breed in clear water of suitable PH, temperature and nutrient composition (Okorie et at, 1978).
Aedes mosquito usually breeds in natural habitats especially in tree holes, leafs axils, rock pools and similar sites (Hawley, 1988). Wide spread deforestation, climate change and increase in global trade has forced this mosquito worldwide to adapt to breeding in domestic and semi-domestic artificial container habitats (Gubler et al, 2001; Delatte et al,2008).

The unplanned and haphazard growth of urban settlement, stagnant water in ditches and drains, cesspits, septic tanks, water tanks, barrels and all sorts of containers have increased the culex breeding surface area (WHO/TDR, 1975).

Culex species are found breeding in fresh water habitats such as pools, ditches, ponds and even in effluents of sewage treatment plants. Ochlerotatus species are found in temporary flood water pools, fresh and brackish marshes, and natural artificial containers. Psorophora species breed primarily in temporary flood water such as woodland pools, road side ditches and pastures. Deranotaenia species are most commonly found in ground pools, swamps and grassy edges of lakes. They feed primarily on reptiles and amphibians and are not known to bite humans (PHPC, 2001).


1.3 Aims And Objectives

The aims and objectives of this study are:

  1. To identify the breeding sites of mosquitoes.
  2. To know the species of mosquitoes that are highly prevalent in Uyo urban.
  3. To determine the physico-chemical parameters of the breeding sites.
  4. To know their various control measures.

Chapter Five


5.0 Conclusion And Recommendation

5.1 Conclusion

In conclusion, Polymerase Chain Reaction (PCR) showed that An. arabiensis is the predominant Anopheles in the study area,the vector is anthropophilic (preference for humans)and endophilic(bites indoors). This may help narrow down vector control measures to a selective, targeted, site specific, ecologically sound and cost effective (malaria) vector control strategy suited to local environmental and epidemiological conditions of the northeastern Nigeria but the same is not easily applicable to South western Nigeria where PCR based test identified a more diverse mosquito fauna. This may have implications on control measures targeting a single species, which will have little impact on malaria infection associated with either An. funestus or An. arabiensis. In the South, the contribution of the three most important afrotropical malaria vectors may account for the perennial malaria transmission, compared to other parts of Nigeria where one vector species predominates and transmission is seasonal. The high number of An. arabiensis caught indoors and the positive sporozoite rate indicate their epidemiological importance in malaria transmission.

Mosquito infection by malaria (Plasmodium) parasites determined using the ELISA method for the detection of Plasmodium falciparum sporozoite protein showed that out of 289 randomly selected Anopheles mosquitoes 7(2.4%) were positive for P. falciparum circumsporozoite antigen. All seven were An. arabiensis indicating susceptibility of An. arabiensis to local strains of the malaria parasite Plasmodium falciparum and its epidemiological importance in malaria transmission in the Sahel.

Mosquito blood feeding preferences was determined by direct ELISA using the Human Blood Index (HBI) which is an indication of the degree of anthropophily showed that the proportion of An.arabiensis with human blood was ninety eight (98%) percent and only two (2%) percent tested positive for bovine blood indicating a tendency to feed on man in preference to other animals (anthropophily as opposed to zoophily). Mosquitoes that prefer human blood to other animals are more dangerous as they more likely to transmit diseases notably malaria. Findings from the longitudinal parasitological study indicated the peak period of malaria transmission as September with the highest Geometric Mean Asexual Parasite Densities (GMPD) of 13,655 asexual parasites per microlitre of blood. This finding is strategic to timely planning and correct application of vector control operations such as Indoor Residual Spraying (IRS) in the study area to prevent seasonal peaks of malaria transmission. The high prevalence of gametocytes amongst the vector age group reservoir (children aged 1-8years). screened during the study indicates the possibility of a continual increase in antimalarial drug resistance in the Sahel.

Though the doses of pyriproxyfen used in this work under field conditions have been shown to produce extended residual activity and much higher inhibition rates but the persistence of pyriproxyfen in water in the absence of organic matter and increased temperature and sunlight declines as was observed in this case. However the important larvicidal potentials of pyriproxyfen at low dose has been demonstrated by this preliminary study. It deserves further consideration as a candidate larvicide for integrated vector management (IVM) in the urban areas of Nigeria. The major interventions for diseases like malaria are indoor residual sprays and the use of long lasting insecticidal treated nets. These do not provide complete control especially in the urban area where recent data indicates that urban m alaria is being associated with the adaptation of An.gambiae s.s to a wide range of polluted water and temporary breeding sites.


5.2 Recommendations

The following recommendations were made

  1. Interruption of vector-human contact is of priority in breaking the transmission chain of malaria parasites. This could be through screening of houses in urban quarters and environmental.
  2. The timing of residual insecticide spraying is crucial in obtaining maximum benefit. This finding is strategic to timely planning and correct application of vector control operations such as Indoor Residual Spraying (IRS) in the study area to prevent seasonal peaks of malaria transmission.
  3. Reduction in the number of gametocyte carriers in the population by the timely use of gametocytocidal anti-malarial drugs such as the dihydroartemisinins in line with World Health Organization recommendation that the use of artemisinin–based combinations (ACTs) as the gold standard antimalarial for managing uncomplicated malaria cases.

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